| Different definitions of and/or approaches to self-esteem |
| Lack of a theoretical framework in some studies |
| Different self-esteem assessment scales |
| Arbitrary (and differing) thresholds applied to the results of the scales |
| Inconsistencies between the theoretical framework and the scale used in some studies |
| Different study populations [40] |
| Different measurement schedules [8,41,42] |
| Design often cross-sectional or post-interventional |
| Losses to follow-up due to attrition [43] |
| Impact of the vocational character of the training [44] |
| Few explanations of the phenomenon (process and reasons for changes in self-esteem, or interaction mechanisms) |